Quadrajet carb and poor miledge

[crawdad]

The best I can do with miledge is about 11 miles per gallon right now (around town) . I've got a 305 CID engine, Q-jet carb, and auto tranny. I've replaced the spark plugs, etc., and adjusted the mixture on the carb. The only problem that I can see is that the carb seems to still be running real rich. The tailpipe is black and the smell of gas is strong sometimes. However, the engine cranks, idles, and runs just fine. Doesn't skip or anything. I'm sure the carb is probably what's causing the poor miledge, but what could be wrong with it that would cause it to be running so rich and what can I do about it? Are the Q-jets fairly easy to rebuild or do I need to start looking for a good carb mechanic? Thanks for any help. (BTW, the truck is the 85 in my sig and it's all stock)

[Zoomad75]

If you have done carbs before, Q-jets are not overly difficult to rebuild. When they are running right, they can be a very effeiciant carb too (provided you can keep your foot out of it).

Couple of things to look at before pulling the carb. Look at your choke adjustment. Could be set a little too much to the rich side of the scale. Do you know if it's the stock carb or one swapped from a 350? The 350's meetering rods/jets/hanger would allow it to run richer than normal too.

If everything as far as the external settings go looks good you might want to go ahead and get a carb kit for it. Get a new float too and an accelerator pump(if it's not part of the kit). Your float might be brass or plastic, either way if it's holding fuel due to a hole or porisity, it would force it to run rich. Take care in pulling it apart, use an old cookie sheet to keep from loosing parts. If you are unsure if you can get it back together, take some good digital pics of all 4 sides before you take it apart so you have it as a guide for re-assembly. Take it slow as a couple of clips and rods are tedious to remove, but it's not hard to do. Once you got it apart clean the throttle body/main body and lid in carb cleaner. Actually dipping the parts in a can of carb cleaner is best, but you can hose it down with spray cleaner too. Use compressed air to dry the parts off. Before you start the re-assembly, you need to check a couple of spots out. 1 Look at the shaft for the primary throttle and where it runs through the throttle body casting. This is a typical wear spot for q-jets as the throttle body bore where the shaft runs through oval out, causing a vaccum leak. If you have wear here, a couple of places sell a kit to drill the throttle body out and install bushings in the casting. 2nd, look at the underside of the main body casting. you should see a couple plugs. These plugs can leak fuel, causing a bump in fuel consumption. Simple fix is to mix up a batch of JB weld and seal up the seam between the plug and the casting. The rest of the rebuild goes simply, just pay attention to your float setting.

One suggestion I would make to anyone that is thinking of tinkering with a q-jet is to head down to the local bookstore and get the book titled: Rochester Carburators. It's published by HP books and is the best for instructions on rebuild and tuning.

[SSC's76]

Rob has some good info here and I see another P.CO person which is cool. I'll give the warning though most q-jets have been taken apart and reassembled soo many times many parts have gotten "lost" and throttle shafts have been worn to a point they need new bushings put in. If you can verifiy that this carb is factory as far as primary jetting goes I'd suspect the casting plugs are leaking like crazy which is the most common reason for poor milage with a Q-jet. They can be kinda difficult to rebuild if its your fisrt time so do as Rob sugests and get the bookand take pics. When you get to the point where you want to rebuild the carb check around with your local welders and see if any of them will silfloss the casting plugs in your carb. It will last a heck of a lot longer then JB Weld.

[crawdad]

Originally Posted by SSC's76

When you get to the point where you want to rebuild the carb check around with your local welders and see if any of them will silfloss the casting plugs in your carb. It will last a heck of a lot longer then JB Weld.

Thank you both for the good information. I got to tell ya though, I've never heard the term "silfloss" before. Sounds like something you would do to your teeth Can you explain what that means? Thanks.

[MylilBowTie]

Originally Posted by Zoomad75

One suggestion I would make to anyone that is thinking of tinkering with a q-jet is to head down to the local bookstore and get the book titled: Rochester Carburators. It's published by HP books and is the best for instructions on rebuild and tuning.

I think Doug Roe is the auther.

[Slonaker]

Originally Posted by MylilBowTie

I think Doug Roe is the auther.

I recently bought the Doug Roe book. It is an excellent resource. I got my copy at Borders bookstore.

Slonaker

[SSC's76]

Originally Posted by crawdad

Thank you both for the good information. I got to tell ya though, I've never heard the term "silfloss" before. Sounds like something you would do to your teeth Can you explain what that means? Thanks.

It's a high strenght silver solder. It's commonly used in metal tube repair to fix cracks in AC/brakes lines ect. It works real well on the casting plugs as long as they are cleaned up it wont come off or leak anytime soon.

I guess you could use it could be used in ones mouth if ya wanna flash the hoochies your custom grill. Stupidest fad ever!

[Zoomad75]

Never heard of the silver-soldering on a carb before. Although, JB weld hasn't leaked on any q-jet my dad or I did. My only suggestion would be making sure the casting is completely dried out of any fuel. Adding heat from soldering could be a potential problem. I would hope that a shop you brought it to would understand that, but good ones are hard to find.

Thats why I like the JB weld method. The key is to let it cure throughly before reassembly.

Either way would work though.

[SSC's76]

JB weld seems to have gone to crap over the past couple years. It never seems to cure correctly since they switched to a new formula.

[skillet]

There was an article in Car Craft of Sept. 2001 about rebuilding a quadra-jet. The guy that did it worked for Jet Performance Fuel Systems in Huntington Beach, CA. jetchip.com. I e-mailed them and asked what they used to seal the casting plugs and they said Devcon, 5 min. 2 part epoxy. I don't know if they use it because it's better than JB Weld or because it's faster for them. I used it on my carb back then, but have'nt taken it apart since to see how it's holding up. My mileage did increase 1 mpg. Never thought of Silflos, just assumed it would melt the carb. Silflos sounds like a better solution, I'll have to try it next time.

[Zoomad75]

Originally Posted by SSC's76

JB weld seems to have gone to crap over the past couple years. It never seems to cure correctly since they switched to a new formula.

Been more than a couple of years since I did a Qjet myself....I had my resident carb expert (my dad) go though the one on my K5. Call me a chicken, but I don't have the patience to do it. I've done them, but Dad's retired and needed something to do for a couple of days.....He's a pro on carbs. From old WCFB's (2x4) on his 57 to webber's on an old Porsche he can do them all. He's working on some old sidedraft carbs from a 54 vette for a guy right now. In my case, let the pro do the work...

All I know is he's got my q-jet dialed in on the money. Starts quick, idles smooth heck even the choke works on its own like it should. (I always mess that up on mine)

[GMC Jim]

Amazon has the Rochester Carb book by Doug Roe for $10.25 and up ( used and new !)

[86k10]

What's so bad about 11 in town, your right in the normal range as far as I know. I used to have a 305 and that's about all it got no matter now much I toyed with the carb. It would get about 16 maybe 17 on the road. You might try going a couple sizes smaller on main jets to see if that helps but it just takes so much gas to run them no matter what you do. You probably have the same trouble I had, to high of gearing.

[crawdad]

Originally Posted by 86k10

You probably have the same trouble I had, to high of gearing.

Nope, it has 2.73 gears. Eleven MPG just sounded a little bit too low.

[Wrenchbender Ret]

One thing you don,t wan,t to do is buy a reman. & give them your old carb. About 3 out of 4 are no good. Do it yourself or get a good carb man to do it. It may have a bad float or the metering rods are stuck in the up position.

[86k10]

2.73? Is the truck your talking about the one in your sig? Those are to high of gears even if you have a 3 speed trans. I would just take your carb and boil it out good and make sure the float isn't getting to heavy and even lower the metering rods by a turn and see if that helps. Make sure the metering piston is free and doesn't bind. I have sanded it and the bore with 600 sandpaper and had good results doing it. You could probably go 2 sizes smaller on your main jets too if you can find some.

[crawdad]

Originally Posted by 86k10

2.73? Is the truck your talking about the one in your sig?

Yep, that's the one. It came from the factory with the 2.73 gears. At least that's whats on my glove box sticker. It's not my daily driver, so I think I'll try to rebuild the carb myself. If I screw it up, I'll buy an Edelbrock intake and carb and be done with it I still think that, considering the engine, tranny and gears, I should be getting better around town miledge than 11 mpg. What are the rest of you getting for miledge around town and open road and what is your setup?